The present invention relates to an optical encoder for detecting the rotations of a motor, etc.
A prior art optical encoder is constructed as shown in FIG. 2 and FIG. 3
In the drawings; housing 20 is attached to and fixed at a mount 23 of a bracket 22 of a motor 21. A rotating shaft 24 is supported at the housing 20 by means of a bearing 25 and is directly connected to the rotating shaft 26 of the motor 21 via a connector 26a. A rotary disk 27 has a pattern (not illustrated) composed of a light shielding portion or a light-penetrating portion attached to a transparent member such as glass that is attached to the rotating shaft 24. A holder 28 is a holder to retain light emitting elements, which is constructed by molding. As shown in FIG. 3, the holder 28 is constructed of a supporting portion 28a attached to the housing 20 and an attaching portion that attaches the light-emitting element 29. The light emitting element 29 is attached so as to be inserted into a hole portion secured at the supporting portion 28a of the holder 28. A sub-board 30 has a photo detector element 31 attached to the plate surface of the sub-board 30. A main board 32 is attached to the housing 20 via a supporting member (not illustrated), and the main board is connected to the sub-board 31 by a connection line (not illustrated), and an electronic component that detects the speed of rotation or position of the rotation is incorporated on the plate surface of the main board 32. A cover 33 covers up the optical encoder and is fixed at the bracket 22 of the motor 21. A lead wire 34 comes out of the optical encoder.
Next, a description is given of an assembly process of an optical encoder.
First, the rotating shaft 24 is attached to the bearing 25 attached to the housing 20, and a rotary disk 27 is fixed at the rotating shaft 24. Next, the sub-board 30 provided with the photo detector element 31 is attached to the housing 20, wherein the holder 28 to which the light emitting element 29 is attached is fixed at the housing 20 so that it is opposed to the photo detector element 31 to accommodate the rotary disk 27 therein.
The optical encoder thus constructed is completed so that the cover 33 surrounding the optical encoder is attached to the bracket 22 of the motor 21 after it is attached on the mounting seat of the bracket 22.
Actually however, since the outer circumferential portion of the rotary disk is made open until the prior art optical encoder is attached to the motor, foreign substances and dust floating in the air may adhere to the rotary disk or foreign substances and/or dust adhered to the cover may drop from the cover due to vibrations during operation and adhere to the rotary disk, thereby making rotation detection impossible.
It is therefore an object of the present invention to provide an optical encoder that is capable of executing accurate rotation detection, free from any adhered foreign substances and/or dust.
In order to solve the abovementioned problems, an optical encoder according to the invention comprises a rotating shaft pivotally supported on a bearing of the housing; a rotary disk fixed at the rotating shaft; a light emitting element attached to the housing; a photo detector element attached to the housing, which can receive light passed through or reflected by the rotary disk from the light emitting element; and a main board incorporating a circuit that detects the speed of rotation and position of rotation from the light received by the photo detector element and is attached to the housing; wherein a holder consisting of a covering portion annularly formed so as to be engaged with the outer circumference of the main board and a light emitting element retaining portion formed at the covering portion is attached to the housing.
Therefore, according to the invention, it is possible to secure a dust-proof structure without hindering the assembly process of an optical encoder and to accurately detect the rotation without permitting foreign substances and/or dust to adhere to the rotary disk.